The present invention generally relates to apparatus and methods of fabricating plastic articles, and particularly relates to apparatus and methods of forming pultruded plastic articles.
Pultrusion is a well-established process for the production of composite material with continuous fiber reinforcement. Such fiber-reinforced materials have been used as dental devices, such as orthodontic archwires. For example, U.S. Pat. No. 5,869,178 to Kusy et al. discloses a pultrusion apparatus configured to form fiber-reinforced polymeric plastic materials having a linear shape.
In K. C. Kennedy and R. P. Kusy, Investigation of Dual-staged Polymerization and Secondary Forming of Photopultruded, Fiber-reinforced, Methacrylate-Copolymer Composites41 J. BIOMED. MATER. RES. at 549 (1998), the authors propose pultruding fibers through a resin comprising benzoin ethyl ether (BEE), 2,2-Bis[4-(2-hydroxy-3-methacyloxypropoxy)phenyl]propane (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), and methyl metha/crylate (MMA) and curing the pultruded fibers to form a partially cured, xcex2-staged composite. Secondary forming of the xcex2-staged composites is accomplished by swaging circular cross-sections into rectangular ones, using a multi-chambered compression mold, while maintaining a constant cross-sectional area. Thermal polymerization of the xcex2-staged composites is conducted within the mold for reformed materials.
U.S. Pat. No. 4,894,012 to Goldberg et al. discusses forming dental appliances directly on a dental cast from preformed bars, strips, or wires using a heat gun. Alternatively, the preformed shape is initially fabricated using a mold that is heated at optimum temperature under pressure in an oven or by a heat gun applying drying heat. The preformed shape may allow arch forms and other complex shapes that more closely approximate the final dental appliance. While the final dental appliance can be made using a male-female mold, the preformed shape used for the final dental appliance may also be formed with a heat gun on the dental cast. The final forming process for a dental appliance may be accomplished using a dental cast, which accurately duplicates both the hard and soft tissues in the mouth. The fiber-reinforced composite strip or bar is sealed or clipped to the cast, and the sections are sequentially heated until soft. Following the softening of the preformed component, the preformed component is molded to the intricate detail of the teeth or soft tissues by hand. The final dental appliance is cooled to room temperature before its removal from the cast.
U.S. Pat. No. 4,462,946 to Goldsworthy proposes an apparatus that receives strands of filament reinforcing material impregnated with a hardenable binder such as a curable resin. The resin-impregnated fiber containing reinforcing strands are disposed about plugs formed from a bulk-molding compound, each of which are draped over a continuous string to form a chain of the plugs on the string. A shrinkable film is wrapped about and encloses each of the strand-encased plugs on the chain. The film is shrunk and a pre-curing device initiates a cure of the curable resin binder impregnated in the strands. The fiber-wrapped, strand-encased composite plugs are introduced into a final mold that contains a pair of split mold elements, which imparts the final shape to each of the articles to be produced. The final mold also applies a curing radiation to the film-wrapped, strand-encased plugs to cure finally the plugs to hardened reinforced plastic composite articles. The shrinkable film is removed, and the final articles are cut into the discrete composite articles.
Various polymeric resins have been described for pultrusion applications. For example, in A. C. Karmaker and A. T. DiBenedetto, Continuous Fiber Reinforced Composite Materials as Alternatives for Metal Alloys Used for Dental Appliances, 11 J. BIOMAT. APPL., at 318 (January 1997), the authors propose fabricating prepregs by pulling glass rovings through a resin bath containing a 50/50 mixture of Bis-GMA and polyethylene glycol dimethacrylate (PEGDMA 200), to which 0.75 weight percent benzoyl peroxide (BPO) was added as an initiator. The prepregs were mounted on a flat plate and transferred to an oven for xcex2-staging.
In T. Chen and R. P. Kusy, Effect of Methacrylic Acid:Methyl Methacrylate Monomer Ratios on Polymerization Rates and Properties of Polymethyl Methacrylates, 36 J. BIOMED. MAT. RES. at 190 (1997), the authors propose five binary formulations that were prepared from methyl methacrylate (MMA) and methacrylic acid (MAA) monomers, and six ternary formulations that were prepared from polysols of polymethyl methacrylate, MMA and MAA. Benzoin ethyl ether (BEE) was used as an ultraviolet initiator.
In Ross P. McKamey and Robert P. Kusy, Stress-relaxing Composite Ligature Wires: Formulations and Characteristics, 69:5 THE ANGLE ORTHODONTIST, at 441 (1999), the authors propose encasing ultra-high molecular weight poly(ethylene) fibers in a poly(n-butyl methacrylate) polymer, formulated from a polysol and an optimal benzoin ethyl ether concentration.
According to one aspect of embodiments of the present invention, a pultrusion apparatus for manufacturing a fiber-reinforced plastic article having a non-linear shape includes a mold configured to receive a partially cured fiber-reinforced plastic article and to form the partially cured fiber-reinforced plastic article into a spirally wound shape. A drive mechanism is coupled to the mold and configured to rotate the mold such that the fiber-reinforced plastic article is taken up on the mold. An energy source is operatively associated with the mold and positioned so that the partially cured fiber-reinforced plastic article is cured in a spirally wound shape as the article is taken up on the longitudinally extending mold.
In embodiments of the present invention, the mold includes a core having a longitudinally extending outer surface, and a longitudinally extending sleeve substantially surrounding a portion of the outer surface of the core. Alternatively, the core and the sleeve may be integrally formed. The longitudinally extending sleeve is configured to provide a first die portion, and may comprise a material, such as a fluoropolymer, which will provide a non-adherent surface. A second die portion is positioned to abut the sleeve such that the first die portion and the second die portion define a die configured to receive the partially cured fiber-reinforced plastic article. In some embodiments, the energy source is positioned downstream from the die, while in other embodiments the energy source is operatively associated with the second die portion. The energy source may be an electromagnetic radiation source and the second die portion may comprise a material that is substantially transparent to electromagnetic radiation emitted by the electromagnetic radiation source.
In other embodiments of the present invention, an alpha-staging apparatus through which one or more fibers are drawn is used to form the partially cured fiber-reinforced plastic article. In still other embodiments of the present invention, the pultrusion apparatus includes a carriage system operatively associated with the mold for maintaining the die and a forming die on the alpha-staging apparatus in substantially vertical alignment with one another. The mold may move longitudinally, laterally, and/or vertically within the carriage system such that the die and the forming die are substantially vertically aligned with one another as the fiber-reinforced plastic article is taken up along a longitudinal portion of the mold.
According to a second aspect of embodiments of the present invention, a pultrusion apparatus for manufacturing a fiber-reinforced plastic article includes a die having a first die portion and a second die portion, and an energy source coupled to the die. At least the second die portion is substantially transparent to energy provided by the energy source so that the fiber-reinforced plastic article is cured by passing energy through the die. The energy source may be an electromagnetic radiation source, which emits electromagnetic radiation in the visible spectrum or the ultraviolet spectrum. The second die portion may comprise a material that is substantially transparent to electromagnetic radiation emitted by the electromagnetic radiation source. The first die portion may also be substantially transparent to energy provided by the energy source or, alternatively, the first die portion may be substantially opaque to energy provided by the energy source.
According to a third aspect of embodiments of the present invention, a method of forming a fiber-reinforced plastic article includes the steps of continuously pultruding a fiber-reinforced plastic article to form a fiber-reinforced plastic article having a first partially cured state, continuously shaping the first fiber-reinforced plastic article having the first partially cured state into a spirally wound shape, and continuously curing the fiber-reinforced plastic article having the first partially cured state to form a spirally wound fiber-reinforced plastic article having a second cured state that is more rigid than the fiber-reinforced plastic article having the first partially cured state. In embodiments of the present invention, the shaping step includes the step of molding the fiber-reinforced plastic article on a rotatable mold. The shaping step may further include the step of drawing the fiber-reinforced plastic article having the first partially cured state through a die having a cross-section to form a fiber-reinforced plastic article having the first partially cured state and substantially having the cross-section. A portion of the rotatable mold may define a portion of the die. The drawing step and the molding step may occur contemporaneously. In other embodiments, the shaping step includes the step of drawing the fiber-reinforced plastic article having the first partially cured state through a die having a cross-section to form a fiber-reinforced plastic article having the first partially cured state and substantially having the cross-section. The curing step and the drawing step may occur simultaneously.
In still other embodiments of the present invention, the curing step includes inputting energy into the fiber-reinforced plastic article and the ratio of the energy input per unit length of the fiber-reinforced plastic article is substantially constant. The energy may be electromagnetic radiation as well as thermal energy. The pultruding step may include the steps of shaping an uncured fiber-reinforced plastic article, and curing the uncured fiber-reinforced plastic article to form the fiber-reinforced plastic article having a first partially cured state. The step of curing the uncured fiber-reinforced article may include inputting a first type of energy into the fiber-reinforced article, and the step of curing the fiber-reinforced plastic article having a first partially cured state may include inputting a second type of energy into the fiber-reinforced plastic article. The first and the second types of energy are preferably different, and are more preferably different types of electromagnetic radiation, for example, ultraviolet radiation and electromagnetic radiation in the visible spectrum.
In a fourth aspect of embodiments of the present invention, a composition of matter includes from about 55 to about 85 percent by weight of a binder, from about 15 to about 45 percent by weight of a diluent monomer, from about 0.05 to about 1 percent by weight of an ultraviolet photoinitiator, from about 0.05 to about 0.5 percent by weight of a visible photoinitiator, and from about 0.05 to about 0.5 percent by weight of an accelerator.
Embodiments of the present invention provide the ability to form a fiber-reinforced composite to a desired shape as part of a continuous manufacturing process. The present invention allows for continuously shaping a spirally wound fiber-reinforced plastic article, obviating the need for any of the work to be done by hand, which may be labor intensive, not as highly reproducible, and potentially contaminating.